The present invention relates to ceramic materials, more particularly to ceramic-ceramic composite materials and methods of making same.
Ceramic materials have seen a variety of applications, including ballistic armor devices, engine parts/components, roller bearings, semiconductors, superconductors, electrical insulators, heat shields, bricks/tiles, orthopedic implants, dental implants, pottery, hot beverage cups/mugs, and statues/figurines/ornaments.
Ceramic materials may be divided into two general groups: oxide ceramics and non-oxide ceramics. The oxides include materials such as aluminum oxide, and are easily prepared by pressureless sintering. The non-oxides, for example tungsten carbide and titanium diboride, have generally higher temperature capability and advanced mechanical properties. These ceramic materials of advanced capabilities (such as involving high toughness or high hardness)—which are in the non-oxide ceramics group—are commonly prepared by pressure-assisted sintering (e.g., hot-pressing), a technique that is not suitable for preparation of an article of complex shape. To the extent that pressureless sintering has been practiced to prepare advanced ceramic materials, this has usually involved the use of a metal sintering aid, which has inevitably resulted in the metal becoming a constituent of the prepared composition and hence altering its properties vis-à-vis the ceramic sans metal. In general, pressure-assisted sintering is limited in terms of reduced production capacity and higher production cost. The need exists in various ceramic-related arts for ceramic materials that are practical and economical for extensive manufacture.
Ballistic armor systems incorporating ceramic material have been used by the military and law enforcement to protect people, stationary structures, and vehicles. Ceramic materials that are especially known to be suitable for ballistic armor applications include aluminum oxide (commonly called “alumina”), silicon carbide, boron carbide, and titanium carbide. These conventional armor ceramics have been developed over the last thirty years or so, represent the current state of the art, and have been relied upon in conventional practice of armor systems—for instance, for protection against impact by a projectile such as a ballistic body (e.g., small arms fire) or an explosive fragment (e.g., shrapnel from a bomb blast).
Conventional ceramic armor materials sometimes fail, or perform less than optimally, when impacted by a projectile. Investigation is continuing in the armor-related arts to improve the capabilities of materials to withstand significant impacts. Furthermore, conventional ceramic armor materials, and armor systems implementing them, tend to be expensive to produce because of the above-noted predominance of pressure-assisted sintering in their preparation.
A “composite” is conventionally understood to mean, in a general sense, a solid whole material composed of at least two solid constituent materials that have different physical characteristics; in the context of the whole material, the constituent materials retain their respective identities and contribute respective properties to the whole material. The terms “two-phase ceramic composite” and “ceramic-ceramic composite” synonymously refer to a composite composed of two different constituent materials that are both ceramic materials. The term “plural-phase ceramic composite” can aptly be applied to a composite composed of two or more different constituent materials each of which is a ceramic material.
Certain two-phase ceramic composites have been demonstrated in testing to have material properties (such as toughness and hardness) that are desirable for armor applications and other applications in which the capability of a material to withstand energy or force is important. See Inna G. Talmy, J. A. Zaykoski, and E. J. Wuchina, “Ceramics in the CrB2-Al2O3 System,” Ceramic Transactions, volume 74, pages 261-272 (1996), incorporated herein by reference. See also Gary A. Gilde, J. W. Adams, M Burkins, M. Motyka, P. J. Patel, E. Chin, M. Sutaria, M. J. Rigali, and L. P. Franks, “Processing Aluminum Oxide/Titanium Diboride Composites for Penetration Resistance,” Ceramic Engineering and Science Proceedings, volume 22, number 3, pages 331-342 (2001), incorporated herein by reference.
Talmy et al. demonstrated that a two-phase composite ceramic material composition consisting of chromium diboride (CrB2) and aluminum oxide (Al2O3) possesses enhanced mechanical properties, as compared with mechanical properties of chromium diboride alone or of aluminum oxide alone. Talmy et al. found an increase in toughness and hardness in various “intermediate” compositions of chromium diboride-aluminum oxide, as compared with pure aluminum oxide or pure chromium diboride. Gilde et al. demonstrated that a two-phase composite ceramic material composition consisting of titanium diboride (TiB2) and aluminum oxide can exhibit enhanced ballistic resistance, especially in terms of penetration resistance, as compared with ballistic resistance exhibited by aluminum oxide alone.
Talmy et al. state on page 263 in their “RESULTS AND DISCUSSION” section: “The optimum hot pressing temperature was 1900° C. for pure CrB2, 1700° C. for Al2O3 and 1800° C. for all the intermediate compositions. Hot-pressed pure CrB2 ceramics exhibited a coarse-grained structure with some closed porosity located both inside the grains and at grain boundaries (Figure 1(a)). Variations in pressing temperature and time did not eliminate porosity. The relative density of CrB2 did not exceed 94%. However, the porosity was significantly decreased by the addition of just 10 mole % (17 vol. %) of Al2O3. The relative density of all materials of intermediate composition increased to 98%. The microstructure of these materials was very uniform.” Talmy et al. state on page 226 in their “SUMMARY” section: “The densification, microstructure, and properties of ceramics in the CrB2/Al2O3 were characterized. The optimum hot pressing temperature was 1900° C. for pure CrB2, 1700° C. for Al2O3 and 1800° C. for all the intermediate compositions. Hot-pressed pure CrB2 ceramics exhibited a coarse-grained structure with some closed porosity located both inside the grains and at the grain boundaries. The porosity was eliminated by the addition of just 10 mole % of Al2O3.”
The term “toughness” conventionally refers to the ability of a material to absorb mechanical energy without breaking, e.g., to deform plastically before fracturing. Toughness involves both strength and ductility. The term “hardness” conventionally refers to the ability of a material to resist change (e.g., scratching or indentation) under mechanical force.